There has hitherto been known a technique of detecting an obstacle in surroundings of a vehicle by use of a sensor such as an imaging device, a sonar, or a millimeter-wave radar mounted in the vehicle, and informing the driver of the detection of the obstacle. For example, Patent Literature 1 discloses a technique of notifying a user of a result of detection by an obstacle sensor such as a millimeter-wave radar as to the presence or absence of a preceding vehicle, or the like.
According to the technique disclosed in Patent Literature 1, the driver can recognize the presence or absence of the preceding vehicle from the detection result of the obstacle sensor. However, the driver just receives the notification of the detection result of the obstacle sensor and thus cannot instinctively grasp at least how much a detection area by the obstacle sensor covers. It is considered that some drivers have desired to grasp at least how much the detection area by the obstacle sensor covers, in order to feel safe.
Further, there has recently been proposed autonomous-driving, such as traveling while automatically following a preceding vehicle, and traveling while automatically keeping a lane. It is considered that during the autonomous-driving, the driver does not perform driving operation, and because of this, the driver has a particularly stronger desire to grasp at least how much the detection area by the obstacle sensor covers, in order to feel safe.